This is a proposal to study various aspects of aqueous humor production and reabsorption using ultrastructural techniques. It consists of four intimately related parts: 1) the analysis of membrane specializations underlying aqueous humor production in the ciliary epithelium; for this, the freeze-fracturing technique will be employed; 2) the analysis of the structures responsible for maintaining the specific composition of aqueous humor. That is, I shall study the ultrastructural counterpart of the blood-aqueous barrier; 3) the analysis of the structural events which result from paracentesis of the anterior chamber or administration of hypertonic agents or prostaglandins; all these procedures have been reported to "break" the blood-aqueous barrier and effect intraocular pressure; 4) the analysis of the mechanisms which control aqueous humor outflow at the sclerocorneal angle, using ultrastructural tracers introduced into the anterior chamber.